The present invention relates generally to a service integrated digital time multiplexed transmission system and specifically to reducing the power requirements of a subscriber terminal in the event of a commercial power outage.
German Offenlegungsschrift [Laid-open Application] No. 2,538,638 discloses an intergrated communications system for the transmission and switching of video, audio and data signals between a central exchange and a subscriber terminal. The subscriber terminal is connected to the central exchange by means of two separate glass fibers, one fiber being used for transmission and the other for reception of telephone and video signals in time multiplex.
U.S. Application Ser. No. 155,132, filed May 30, 1980 now U.S. Pat. No. 4,491,180 by Hans Schussler discloses a service integrated communications transmission and switching system for audio, video and data signals in which only one light conductive fiber is used for the subscriber terminal line. Narrowband services are provided by means of digital transmission in time multiplex mode at the subscriber and the broadband services are provided by means of analog transmission.
In neither of the above systems in there any disclosure relating to the current supply for the devices at the subscriber's terminal. In present-day transmission systems, the devices at the subscriber's terminal are fed by the central exchange battery or power supply through connecting lines to the subscriber. In future optical transmission systems, it will probably not be possible to continue supplying power from the central exchange, since the addition of copper wires in the glass fiber cable constitutes a technical regression and the transmission of electrical energy over a distance of many kilometers by optical means would create power loss and other problems.